This invention relates to a d-c power supply for producing non-interruptible d-c power for energizing a load to ensure continuous uninterrupted operation thereof, the d-c power being derived from a primary power source which may fail from time to time. The primary power source may take a variety of different forms, such as an a-c line voltage source, a gasoline engine-driven generator, a solar powered generator, a wind-driven generator, etc. The invention will be described in an environment where the non-interruptible d-c power is derived from a-c line voltage.
Many loads, including microcomputers or microprocessors, require the continuous application of an operating potential of relatively fixed magnitude to operate properly. If there is a power loss, even though momentary, the operation of a microcomputer will be deleteriously affected. For example, the memory devices may store false information that was not there originally. Moreover, when power is restored, the microcomputer could receive erroneous command signals. Hence, it is most desirable that d-c power be constantly supplied to a microcomputer so that it will not adversely suffer from a loss of primary power, or a-c line voltage in the illustrated embodiment.
In many cases where a load requires non-interruptible d-c power, backup power is available from a standby rechargeable battery. With such a battery backup system, the battery will usually be connected to the load automatically in response to a power outage. Unfortunately, when the switchover or substitution of power supplies occurs, there may be a momentary voltage drop or transient that could disrupt the operation of the load, particularly when the load is a microprocessor. In addition, after the battery is connected to the load the battery voltage may decrease rapidly if the ampere-hour capacity has not been maintained. Many rechargeable batteries must be allowed to go through their charge-discharge cycles to maintain their ampere-hour capacity.
The present invention overcomes the shortcomings of prior backup arrangements by providing a d-c voltage source which is energized by a primary power source and yet there is absolutely no change in the d-c voltage when a failure or low voltage transient occurs in the primary source. The unique d-c power supply of the invention is of relatively simple and inexpensive construction, employing backup power from a battery that will always be at full ampere-hour capacity.